Earlier this year I reported the launch of Starbucks' branded mobile payment system. A couple of months down the road, and millions are getting their caffeine fix with a wave of their mobile device.

In January, Starbucks rolled out mobile payments to 6,800 of its stores and around 1,000 Target-based locations after successful tests in Seattle, Northern California, New York and hundreds of select Target stores across the U.S.

The mobile payment service can be used by Starbucks customers who download the free Starbucks Card mobile app. After crediting the card via credit card users can pay for their cappuccino or frappe with a simple wave of their mobile in front of a scanner at the checkout.

According to USA Today, Starbucks' mobile payment service has been a real hit with customers. Starbucks' CEO Howard Shultz announced to shareholders last week that three million customers had so far used it.

At the time of writing no Android version of Starbucks' app is available.